Polarization dependence of the resonant two-photon ionization spectra of jet-cooled(1R,2R)-(-)-pseudoephedrine

摘要

The polarization dependence of the resonant two-photon ionization(R2PI)spectra of jet-cooled(1R,2R)-(-)-pseudoephedrine was investigated near the origin bands of three conformers.To obtain the difference R2PI spectra of the origin bands,R2PI signals produced by circularly polarized light(CP)were subtracted from those produced by linearly polarized light(LP),which revealed positive values for the P and R branches of the origin bands and negative values for the Q branch.To understand the different polarization behaviors of the P,Q,and R branches,expressions were derived to predict the transition probabilities of symmetric top molecules in a parallel transition.The transition probabilities varied depending on the direction of the total angular momentum J with respect to the light propagation vector.The different polarization behaviors of the rotational branches may arise from the differences in the angular distributions of the J vectors that are preferentially excited by LP and CP.